During exposure to radon, the radiation dose in the lungs is almost entirely due to the inhalation of particulate radon daughter products. These daughter products deposit in the airways of the lungs and irradiate the basal cells of tracheobronchial and pulmonary epithelia. These cells receive doses not only from the deposited progeny but also from the alpha radiation emitted by the radon daughter products formed after deposition.
This knowledge led to the concept of relating radiation inhalation hazards to the ultimate or potential alpha energy concentrations in working level units (WL). One WL is defined as the potential alpha energy concentration from the decay products of radon equivalent to 135,000 MeV per liter of air. It has been shown that one WL also corresponds to 16,844 alpha from radon progeny contained in one liter of air. An RPISU (radon progeny integrating sampling unit) is a generic name given to instruments that collect radon progeny on filter paper and register the alpha radiation from the deposited progeny during an entire period of collection. An RPISU is an instrument designed to measure radon progeny concentration in WL units. Alpha radiation is registered not only during the entire period of collection, but also three hours after cessation of sampling. This data, along with the volume of the sample collected, is converted into a progeny concentration in WL units. RPISU units have been reported that use thermoluminiscent dosimeters, alpha track detectors, and solid-state detectors.
The sensitivities of current systems are restricted by the fact that (1) the detectors are small and must be located close to the filter, within the range of alpha radiation, and (2) the area of filter paper is limited by the size of the detectors.
Previous methods of measuring radon progeny are costly, cumbersome and require large measurement times. Currently, only highly expensive radon progeny monitors are available to measure radon progeny concentrations. In addition, these techniques require a skilled operator to extract meaningful measurements. These involve standard electronic components, which are subjected to effects of temperature, humidity and susceptibility to shocks.
United States Environmental Protection Agency has stipulated that a measurement has to be done for a minimum of two days. Because of diurnal variations, only such measurements are considered as valid measurement for homes.
There are needs for researchers to be able to measure radiation over shorter or longer than two-day periods with simple and efficient devices.